Exhaust gas recirculation valves for the recirculation of exhaust gas quantities adjusted to the respective operating state of the internal combustion engine in order to reduce environmentally harmful portions, in particular, nitrogen oxides, in the exhaust gas of an internal combustion engine are generally known and are described in a large number of applications. These exhaust gas recirculation valves typically comprise an actuator operatively connected with a valve rod which is guided in a housing of the valve by means of a guide bushing and comprises, at its end remote from the actuator, at least one valve closing body corresponding to a respective valve seat. Most such exhaust gas recirculation valves are configured such that, in the closed state of the valve, the guide bushing is located in the region containing fresh air and is separated from the exhaust gas side by the valve closing body. When the valve is opened (i.e., the valve closing body is lifted from the valve seat), however, exhaust gas flows in the direction of the intake pipe so that a connection is allowed between the exhaust gas, charged with soot or other caking and sticky substances, and the guide bushing, whereby, not least because of the temperature differences, accretions are formed on the valve rod and in the guide bushing, respectively, that can affect the functioning of the valve.
Various suggestions have been made to avoid such accretions on the valve rod and in the guide bushing, but also in the interest of preventing functional disorders of electric components in the vicinity of the actuator, such as electromagnets, electric motors or potentiometers, by exhaust gas components.
In order to avoid the ingression of dirt particles into the vicinity of the actuator, DE 103 36 976 describes providing a valve rod seal in the form of a radial sealing ring. Such a valve rod seal is, however, worn after a short operating time and thus loses its sealing function since accretions between the guide bushing and the valve rod cause scratching in the valve rod in the region adjacent to the sealing ring. These possibly sharp edges are passed along the sealing ring and may in turn cause small tears. Leakiness and/or jamming of the valve may result.
Another form of sealing is described in DE 43 38 192 A1. With the valve disclosed therein, a rib is arranged in the region of the clean gas side, which rib is supposed to protect the guide body from thermal radiation and soiling. The valve rod is additionally connected with an elastic membrane that is to seal the control chamber from the exhaust gas outlet. Such a design is a rather complex structure, however, since a plurality of additional components must be used to seal the valve body. The provision of the sealing membrane, in particular, requires additional assembling effort and the production costs caused by a housing with a rib are higher than for a housing without a rib. Accretions moreover accumulate in the region between the guide bushing and the valve rod that lead to a jamming of the valve.
A drawback of the known embodiments is that dirt particles entering between the guide bushing and the valve rod cause functional disorders of the valve by the formation of ridges or scratches in the valve rod or by the accretions themselves. This may also affect the protection of the actuator from dirt particles, resulting in malfunctions of the electric components.